Code360 powered by Coding Ninjas X Naukri.com. Code360 powered by Coding Ninjas X Naukri.com
Table of contents
1.
Introduction
2.
The Functions of a Loader
2.1.
1. Allocation
2.2.
2. Linking
2.3.
3. Relocation
2.4.
4. Loading
3.
What is an Absolute Loader?
4.
Key Characteristics
5.
Algorithm of an Absolute Loader
6.
Frequently Asked Questions
6.1.
What is a Loader and Why is it Important in Computer Systems?
6.2.
How Does a Loader Differ from a Compiler or an Assembler?
6.3.
Are There Different Types of Loaders, and How Do They Vary?
7.
Conclusion
Last Updated: May 6, 2024
Easy

What is Loader?

Master Python: Predicting weather forecasts
Speaker
Ashwin Goyal
Product Manager @

Introduction

Loaders play a crucial role in the realm of computer programming and systems development. They are essential components that enable the execution of object code by a computer. In essence, a loader is a program that loads machine code of another program into the memory, preparing it for execution. By doing so, it becomes an integral part of the process of turning source code into an executable program.

What is loader?

Understanding how loaders work and their various types, including the Absolute Loader, is vital for anyone delving into the technical aspects of computer science and programming.

The Functions of a Loader

A loader typically performs four key functions, each critical to the process of program execution. These functions include allocation, linking, relocation, and loading. We will explore each of these functions in detail.

1. Allocation

Explanation:

Allocation is the first step in the loading process. Here, the loader assigns memory space to the various modules of the program that needs to be executed. This process involves determining the size of each module and ensuring that the necessary memory is available. Allocation is crucial because it prevents overlapping of modules in memory, thereby avoiding data corruption and execution errors.
 

Example:

Consider a program divided into modules A, B, and C. The loader will first assess the size of each module and then allocate appropriate memory segments to them. If module A requires 10KB, module B 20KB, and module C 15KB, the loader allocates memory accordingly, ensuring that these modules do not overlap in the system’s memory space.

2. Linking

Explanation:

Linking is the process of combining various modules of a program and resolving external references between them. The loader links these modules by replacing symbolic references or addresses in the program with actual physical addresses in memory.
 

Example:

If module A has a function that is referenced in module B, the loader resolves this reference by finding the physical address of the function in module A and updating the reference in module B to this address.

3. Relocation

Explanation:

Relocation involves adjusting the module's addresses, allowing them to be loaded at an appropriate location in memory. It is necessary because a program might not always be loaded into the same memory location; thus, the loader must modify the absolute addresses to the current allocated addresses.
 

Example:

If a program is initially written to start at memory location 1000, but during execution, it needs to be loaded at location 2000, the loader adjusts all the program’s addresses by adding 1000 to the original addresses.

4. Loading

Explanation:

The final step is the actual loading of the program into memory. The loader copies the program's machine code from the storage into the system's memory, preparing it for execution by the CPU.
 

Example:

Once the previous steps are completed, the loader takes the machine code of the program and places it into the allocated memory space, ready for the CPU to execute.

Get the tech career you deserve, faster!
Connect with our expert counsellors to understand how to hack your way to success
User rating 4.7/5
1:1 doubt support
95% placement record
Akash Pal
Senior Software Engineer
326% Hike After Job Bootcamp
Himanshu Gusain
Programmer Analyst
32 LPA After Job Bootcamp
After Job
Bootcamp

What is an Absolute Loader?

An Absolute Loader is a simple type of program loader used in computing. Its primary function is to load an executable program into memory for execution without performing any modifications, relocation, or linking. 

Loader

It assumes that the program is already in machine language format and the addresses within the code are already absolute, meaning they are final and will not change.

Key Characteristics

Simplicity: It directly loads the program into a specific memory address without any complex processing.

Fixed Memory Address: Programs are loaded into a predetermined memory location.

No Relocation or Linking: It does not adjust or alter the program's addresses, nor does it link different modules of the program.

Algorithm of an Absolute Loader

Here is a simplified algorithm describing how an Absolute Loader operates:

  • Start: Initialize the loader program.
     
  • Open Object File: Access the object file containing the absolute machine code of the program.
     
  • Read Object File: Sequentially read the contents (machine code) of the object file.
     
  • Load into Memory: Directly load the read machine code into a predetermined memory location specified in the code.
     
  • Verify Loading: Optionally, check to ensure the program is correctly loaded into memory.
     
  • Transfer Control: Transfer the control of the processor to the loaded program, starting from its entry point.
     
  • End: Conclude the loading process.

Frequently Asked Questions

What is a Loader and Why is it Important in Computer Systems?

A loader is a system program that loads executable programs into memory, preparing them for execution. It's essential in computer systems because it bridges the gap between machine code and executable programs. Without the loader, programs written in high-level languages or assembly language could not be executed by the system.

How Does a Loader Differ from a Compiler or an Assembler?

 A compiler or an assembler translates high-level code or assembly code into machine code, while a loader takes this machine code and loads it into the system's memory for execution. The compiler and assembler deal with code translation, whereas the loader is responsible for the actual implementation of the program.

Are There Different Types of Loaders, and How Do They Vary?

Yes, there are several types of loaders, including Absolute Loaders, Relocating Loaders, and Dynamic Linking Loaders. Absolute Loaders load programs into a specific, fixed memory location and don't modify the code. Relocating Loaders, on the other hand, can modify the program's addresses, adapting them to the available memory space. Dynamic Linking Loaders allow for the loading of modules at runtime and can link various modules of a program during execution.

Conclusion

Loaders play a vital role in the functionality of computer systems, serving as the final step in the journey from code to execution. They are crucial for bringing programs to life, enabling the CPU to execute written code. Understanding different types of loaders, their functions, and their importance in various computing environments provides valuable insight into the inner workings of computer systems. As technology evolves, the role and capabilities of loaders continue to adapt, maintaining their essential position in the process of executing programs.

You can refer to our guided paths on the Coding Ninjas. You can check our course to learn more about DSADBMSCompetitive ProgrammingPythonJavaJavaScript, etc. 

Also, check out some of the Guided Paths on topics such as Data Structure and AlgorithmsCompetitive ProgrammingOperating SystemsComputer Networks, DBMSSystem Design, etc., as well as some Contests, Test Series, and Interview Experiences curated by top Industry Experts.

Previous article
CPU Scheduling || Part-2
Next article
Memory Management in Operating System (OS)
Live masterclass